On Lagrangian particles tracking in coastal areas: hydrostatic vs non-hydrostatic model runs

This work is focussed on modelling of the hydrodynamic processes in small coastal areas using a 3-D model on unstructured mesh with fine spatial resolution. A finite element based three-dimensional baroclinic model TELEMAC-3D was applied to the Himmerfjärden area in the Baltic Sea. The TELEMAC modelling suite is developed by the National Laboratory of Hydraulics and Environment (LNHE) of Electricité de France (EDF).

Himmerfjärden is a coastal fjord-like bay situated in the north-western part of the Baltic Sea. The fjord size is 25km by 50km and it has a mean depth of 17m and a maximum depth of 52m. The water is brackish (6‰) with small salinity fluctuation (±2‰). A sewage treatment plant, which serves about 300 000 people, discharges into the inner part of Himmerfjärden.

The modelling domain is approximated by unstructured mesh with element size varying from 50m along the coast to 300m offshore. In vertical direction 20 sigma layers were used. The area was modelled operationally for five days period using model in hydrostatic and non-hydrostatic modes. Open boundary conditions were obtained from the Baltic wide NEMO v4.0 model operationally running by SMHI and provided by the Copernicus Marine Service. Meteorological forecast data were obtained using Open-Meteo API (https://open-meteo.com). Lagrangian particles were tracked online with and without stochastic diffusion.

The computations were enabled by resources provided by the Swedish National Infrastructure for Computing (SNIC) at the NSC - National Supercomputer Centre at Linköping University, partially funded by the Swedish Research Council through grant agreement no. 2018-05973.